Add UMA histograms for WebAudio

third_party/WebKit/Source/modules/webaudio/OfflineAudioContext.cpp

Index: third_party/WebKit/Source/modules/webaudio/OfflineAudioContext.cpp
diff --git a/third_party/WebKit/Source/modules/webaudio/OfflineAudioContext.cpp b/third_party/WebKit/Source/modules/webaudio/OfflineAudioContext.cpp
index dc3afb966c3be24c02b0a5c034ddb0727f8a75d7..9b0e0cd2411d6b7d2c679e1ef453092f1c028719 100644
--- a/third_party/WebKit/Source/modules/webaudio/OfflineAudioContext.cpp
+++ b/third_party/WebKit/Source/modules/webaudio/OfflineAudioContext.cpp
@@ -35,6 +35,7 @@
 #include "modules/webaudio/OfflineAudioCompletionEvent.h"
 #include "modules/webaudio/OfflineAudioDestinationNode.h"
 
+#include "platform/Histogram.h"
 #include "platform/audio/AudioUtilities.h"
 
 namespace blink {
@@ -90,6 +91,27 @@ OfflineAudioContext* OfflineAudioContext::create(ExecutionContext* context, unsi
             + ")");
     }
 
+    DEFINE_STATIC_LOCAL(SparseHistogram, offlineContextChannelCountHistogram,
+        ("WebAudio.OfflineAudioContext.ChannelCount"));
+    DEFINE_STATIC_LOCAL(SparseHistogram, offlineContextLengthHistogram,
+        ("WebAudio.OfflineAudioContext.Length"));
+    DEFINE_STATIC_LOCAL(SparseHistogram, offlineContextSampleRateHistogram,
+        ("WebAudio.OfflineAudioContext.SampleRate"));
+
+    offlineContextChannelCountHistogram.sample(numberOfChannels);
+    // To limit the size of the histogram, record 10*log10(numberOfFrames),
+    // clipping the value at 60 (buffer size of 1 million frames). This
+    // gives 60 entries in the histogram.
+    double histogramValue = 10*log10(numberOfFrames);
+    offlineContextLengthHistogram.sample(clampTo(static_cast<int>(0.5 + histogramValue), 0, 60));
+
+    // To limit the size of the histogram, record
+    // 40+10*log2(sampleRate/48000), clipping the value to lie between 0
+    // and 60.  These limits correspond to a min rate of 3000 and a max of
+    // 192000.  This gives 60 entries in the histogram.
+    histogramValue = 40 + 10*log2(sampleRate / 48000);
+    offlineContextSampleRateHistogram.sample(clampTo(static_cast<int>(0.5 + histogramValue), 0, 60));
+
     audioContext->suspendIfNeeded();
     return audioContext;
 }